Pulse position dial receiver employing pulse superposition for identifying digits



Oct. 28, 1952 w. A. MALTHANER ET Al. 2,615,971

PULSE POSITION DIAL RECEIVER EMPLOYING PULSE SUPERPOSITION FOR IDENTIFYING DIGITS 15 Sheets-Sheet 1 Filed Dec. 30, 1948 N y uw w .m A1; V T A H.. y@ B Oct. 28, 1952 w. A. MALTHANER ETAL. 2,615,971

` PULSE POSITION DIAL. RECEIVER EMPLOYING PULSE SUPERPOSITION FOR IDENTIFYING DIGITS Filed Dec. so, 194e 15 Sheets-Sheet 2 mdm/ M A MAL THANER /Nl/E N TORSN. D. NEWBY HE. VAUGHAN A T TORNE V Oct. 28, 1952 w. A. MALTHANER ETAL 2,615,971

PULSE POSITION DIAL RECEIVER EMPLOYING PULSE SUPERPOSITION FOR IDENTIFYING DIGITS Filed Deo. 30, 1948 1 13' Sheets-Sheet 3 naar [430 Hl cH n. A. MALTHANER /Nl/E/VTO RS N. D. NE WBV H E. VA UGHN Oct- 28, 1952 w. A. MALrHANER. ETAL 2,615,971

PULSE POSITION DIAL RECEIVER EMPLOYING PULSE SUPERPOSITION FOR IDENTIFYING DIGITS Filed Dec. 30. 1948- 13 Sheets-Sheet 4 MAGNET/C RECOROE'R P/CK U RECORD/NG co/L Y PERMANENT MAGNET ERASER W.A.MALTHANER /NVE N TOPS N. D. NEWBY H. 5. v4 06f-IAN m Wl ATTORNEY Oct. 28, 1952 Filed Dec. 30, 1948 W. A. PULSE POSITION D MALTHANER ET AL IAL. RECEIVER EMPLOYING PULSE SUPERFOSITION FOR IDENTIFYING DIGITS 13 Sheets-Sheet 5 W A. MALTHNER MD. NEWBY H E. VAL/CHAN ATTORNEY /A/l/NTORS Oct. 28, 1952 w. A. MALTHAN'ER ETAL 2,615,971

PULSE POSITION DIAL RECEIVER EMPLOYING PULSE SUPERPOSITION FOR IDENTIFYING DIGITS 15 sheets-'sheet e Filed Dec. 30, 1948 Oct. 28, 1952 w. A. MALTHANER ETAL 2,615,971

' PULSE POSITION DIAL. RECEIVER EMPLOYING PULSE SUPERPOSITION FOR IDENTIFYING DIGITS Filed DSC. 30.71948 13 Sheets-Sheet 7 PV. A. MAL THANER 02 /Nl/E/VTORS: Ma/vfwsr By HE. VAUGHAN M Maf/LM A T TUD/UFV Oct. 28, 1952 w. A. MALTHANER ETAL 2,515,971

PULSE POSITION DIAL RECEIVER EMPLOYING PULSE suPERPosITIoN FoR IDENTIFYING DIGITs Filed nec. so. 1948 .1s sheets-sheet a RL E :of f A. MAL THA/VER 0 w /NVENTORS N. D. /vfwr d By HEL/AUGHA/v A T TORNE y 13 Sheets-Sheet 9 W. A. MALTHANER ET AL PULSE POSITION DIAL RECEIVER EMPLOYING PULSE SUPERPOSITION FOR IDENTIFYING DIGITS VVV Oct. 28, 1952 Filed Dec. 3o) 1948 H E. VAUGHA/V I, W M

Oct. 28, 1952 w. A. MALTHNER ETAL 2,615,971

PULSE POSITION DIAL RECEIVER EMPLOYING PULSE SUPERFOSITION FOR IDENTIFYING DIGITS Filed Dec. 50, 1948 15 Sheets-Sheet 10 `W A. MAL'THANER /N VE N TORS N. D. NEWBY H. E. VUGHAN FIG /NITEGRA Tof? co/v 7R01.

A 7` TOPNEV Oct. 28, 1952 w. A. MALTHANER ETAL 2,615,971

PULSE POSITION DIAL. RECEIVER EMPLOYING PULSE SUPERPOSITION FOR IDENTIF'YING DIGITS v Filed Dec. so. 194e 1s sheets-sheet 11 Ot. 28, 1952 w. A. MALTHANER ETAL 2,615,971 4 PULSE POSITION DIAL'ARECEIVER EMPLOYING PULSE SURERPOSITION FOR -IDENTIFYAING DIGITS. Filed Dec. 30, 1948 l5 Sheets-Sheet 12 WA. MALTHA/VER /NVENm/PS M NE WBV h1 E. VUGHAN ATTORNEY Oct. 28, 1952 w. A. MALTHANER ETAL 2,615,971

PULSE POSITION DIAL RECEIVER EMPLOYING PULSE SUPERPOSITION FOR IDENTIF'YING DIGITS l5 Sheets-Sheet 13 Filed Dec. 30, 1948 W.' A. MALTHA/VEH /A/l/E/VTORSN. 0. NEWBV H. E. VAUGHAN Patented Oct. 28, 1952 PULSE POSITION DIAL RECEIVER EMPLY1 ING PULSE SUPERPOSITION FOR IDEN'IL FYING DIGITS William A. Malthaner, Su

mmit, Neal D; Newby,

Leonia, and Henry E. Vaughan, Chatham, N. J., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a. corporation of New York Application December 30. 1948, Serial NQ, 68,234 17 Claims. (Cl. 1772+353) This invention relates to calling and signaling methods, apparatus and systems, and more particularly to improvements in the methods, apparatus and systems disclosed in the patent application of Malthaner-Newby-Vaughan, filed on or about June 29, 1948, Serial No. 35,924.

Signaling and calling arrangements in accordance with the present invention may be advantageously employed in automatic telephone switching systems wherein a subscriber initiates a call and directs automatic switching equipment at distant switching points to establish connections to desired called partys line.

More particularly, the present invention is directed to calling equipment and methods of operation thereof in which each element or digital position of a called subscribers designation is represented by two pulses of short duration Which may be readily transmitted over voice frequency communication paths and in which the time interval elapsing between the two pulses represents the numerical value of the digit or the characteristics of the symbol.

In accordance with the exemplary embodiment of the invention set forth in detail herein the signaling or calling pulses represent subscribers designations. In many types of telephone switching systems these designations comprise a multidigit number which frequently includes an oice designation of one or more letters or numbers or a combination of letters and numbers followed by a multidigit line number. These designations are in turn sometimes followed by another letter or number which is frequently employed to designate the particular party connected to a party line.

It is, of course, possible to designate called subscribers station by any suitable symbol or group of symbols forming a code or station designation.

In order that these designations may be more readiiy referred to it is assumed that each designation comprises a number of elements Which in the exemplary embodiment set forth is eight.

Each of these elements is referred to herein as a symbol or digit. In order to avoid further ambiguity in describing the operation of the system in response to the various signals representing the symbols or digits the designation will be describe-.i as comprising a number of digital positions, that is eight digital positions in the exemplary embodiment set forth herein, and each of the digits or symbols in each of the digital positions or symbol positions may comprise a digit of any ,one of a plurality .of different magnitudes 2 or may comprise symbols in any one of a plurality of different characteristics.

Each of the pulses transmitted is of suciently short duration so that it may be readily transmitted over voice frequency communication paths, through repeating coils, filters, amplifiers, and other equipment associated with voice frequency communication paths. These pulses may be also transmitted through modulating equipment and then over carrier current and radio systems in the same manner as voice frequency currents, as is well understood.

The arrangement set forth herein in detail is designed to cooperate with a source of such pulses representing the number or designation of the called station which is transmitted repetitively. A suitable form of puls@ generating equipment for generating pulses at the subscribers station with which the exemplary embodiment set forth herein is designed to cooperate is disclosed in an application of Parkinson, filed on or about June 29, 1948, Serial No. 35,930.

In order to operate such signaling or calling equipment at the subscribers station, it is frequently necessary to supply operating power over the subscribers line and employ a filter or filters to separate the power frequency from the signaling frequencies. Such a filter or lters together with transmission systems frequently encountered in telephone transmission networks frequently cause distortion of the signaling pulses.

The arrangement set forth in the above-identi- -ed application of Malthaner et al., Serial No. 35,924, led June 29, 1948 employs amplitude responsive means for recognizing a received pulse. In other words, when the amplitude of the power, cur-rent, voltage or other signiiicant characteristic of the received rpulse exceeds a predetermined reference value the equipment responds thereto and indicates the reception of a pulse at that time. In employing such an arrangement over long carrier -systems including long carrier current systems, excessive distortion is frequently encountered which distortion renders such indications of received pulses unreliable.` l Y Y It is an object of the present invention to provide methods, apparatus andv circuits to overcome these diiiiculties by comparing the two pulses representing each element of digital position of the subscribers designation VInasmuch as both pulses are transmitted over the same transmission path they are subject to the same `attenuation and usually to the same types of ,distortion so that more reliable opera-tion may be obtained when such pulses are received and compared.

However, in extreme cases, even though both pulses are transmitted over the same transmission path and are attenuated thereby, the phase distortion may vary from instant to instant and thus from pulse to pulse and produce a suicient change in the wave forms of two successive pulses so that it is unreliable to compare the amplitudes oi the two pulses at any given corresponding interval of time within the respective pulse intervals. Such types of distortion are encountered in long carrier current systems due in part to slight differences in the frequencies applied for modulating and for demodulating the signals in single sideband carrier systems.

It is an object of the present invention to provide methods, apparatus and circuits to overcome these difficulties by comparing the pulses representing each element or digital position of the subscribers designation for a substantial portion of the pulse interval which portion may include the entire pulse interval.

An object of this invention is to compare two pulses by deriving a voltage, current, or other electrical quantity from a significant characteristie of each of the pulses such as power, current, or voltage, taking the diierence between the values of the quantity derived from the two pulses and then integrating the absolute value of this diiierence over a substantial or major portion of an entire pulse interval. The presence of the pulses is then determined by the magnitude of said sum of integration.

A feature of this invention relates to the use of a full wave rectier or its equivalent to obtain the absolute magnitude of an electrical voltage or current. Another feature of this invention relates to the use of a full wave rectifier or its equivalent in combination with an electrical storage device such as a condenser to integrate the absolute magnitude, without regard to sign or polarity, of an electrical quantity such as a current, over a predetermined interval of time.

An object of this invention is to combine or take the diierence between a reference pulse and a pulse representing an element or digital identity of a subscribers designation by delaying one of these pulses by different times and then comparing the various delayed pulses with the other duration time of one of said pulses and then selecting the pulses in which said integrated sum does not exceed a predetermined reference value.

A feature of this invention relates to applying pulses to a plurality of delay devices or paths, each having a different delay interval of time which delay intervals or times are equal to or a function of the possible expected different time intervals between the pulses representing the elements or character of a subscribers designation. The output of each of the delay devices is then combined with an undelayed stop pulse in such a manner that the undelayed stop pulse will effectively cancel for substantially the entire pulse duration the delayed start pulse in one and only one of said delay devices. The device or delay path in which the stop pulse cancels the delayed start pulse designates the magnitude of the digit or identifies the character or symbol of a subscribers designation represented by the pulses.

Cil

A feature of the invention relates to a mechanical storing and delay device comprising a rotating magnetic disc, a recording coil located near the periphery of said disc and a plurality of pick-up coils spaced around the rotating disc for providing different delay intervals and a magnetic erasing means for era-sing previously recorded signals and preparing the disc for recording of subsequent signals.

In Systems of the type set forth herein in detail, it is necessary to distinguish or recognize the beginning of each station designation so that the digits may be placed in their proper position in the called subscribers designation. In order that this may be accomplished the calling equipment at the subscribers station is arranged to interpose delays or pauses, frequently called blanks, in the transmission of signals between each series of pulses or signals representing a complete subscribers designation.

A feature of the present invention is directed to means for recognizing these pauses or blanks and conditioning receiving equipment in response to such pauses to receive the following series of pulses designating the called subscribers station.

Another feature of the present invention relates to apparatus for checking that upon the reception of two pulses a digit is properly identied for predetermined ones of the digits of a subscribers number and employing the complete set of pulses recorded after two pulses properly identify a digit for each of said predetermined digits and for disregarding the complete set of pulses in case more or less than two pulses are received for each of said predetermined digits.

Another feature relates to circuits and apparatus and methods of operation for picking out or selecting certain digital positions of a subscribers designation to control the switching circuits or apparatus at any switching position or station.

Another feature is directed to circuits, apparatus and methods for repeatedly resetting the receiver and related switching circuits between series of pulses representing complete called subscribers designation.

Another feature relates to circuits and switching equipment for directing the response of the receiving equipment to each group of pulses representing a symbol or digit to recording or storing circuits or apparatus.

The foregoing and other objects and other features of this invention, the novel features of which are pointed out in the claims appended hereto may be more readily understood from the following description of an exemplary embodiment of this invention when read with reference to the attached drawings in which:

Fig. 1 outlines broadly certain elements of an exemplary system and the manner in which they cooperate one with another;

Fig 2 shows the manner in which Figs. 3 through 12 are positioned adjacent one another;

Figs. 3 through 12 when positioned as shown in Fig. 2 show in detail the various circuits of an exemplary embodiment of the invention; and

Figs. 13 and 14 show graphs of the voltages or currents at various points in the system.

The exemplary embodiment set forth herein is arranged to cooperate with pulse transmitting equipment for transmitting calling signals such as disclosed in the above-identied application of Parkinson the disclosure of which is hereby made a part of the present application by referenoe to the same extent as if set forth in full herein.

The receiver in. accordance with the exemplary embodiment of the invention described in detail herein is arranged to form a part of and cooperate with the other elements of a complete telephone switching system of the type disclosed in a patent application of Malthaner iiled on or about June 29, 1948, Serial No. 35,925. The disclosure of the above-identified Malthaner application is also hereby made a part of this application by reference to the same extent as if the disclosure of said application were set forth in full herein.

As shown in Fig. 1 the incomingr line [0| normally terminates at a resistor |02. This resistor properly terminates the line and tends to suppress stray currents and transients which may be received from the incoming line due to switching and other disturbances. When it is desired to receive incoming signals the receiver is conditioned by operating switch |08 or by automatic equipment which applies ground to lead |08 and causes relay |05 to operate.

The line incoming to the receiver at this time is extended to the subscribers station through suitable switching circuits and devices and over the subscribers line from the central station to the subscribers station. For purposes of receiving signals or calling pulses from the subscribers station from calling apparatus such as disclosed in the above-identified application Parkinson et al., the paths from the central station to the subscribers station need not transmit direct current. It is suflicient if thisv line will transmit voice frequency currents having a bandwidth of from approximately 300k cycles to 2,000 cycles. This bandwidth, of course, may be wider or narrower in certain cases but such a width is suitable and frequently encountered in telephone networks.

The circuit for the operation of relay extends from battery through the winding of relay |05, back contacts on relays 14| and |42 to ground through the operated contacts of key |38 or to other ground applied to the same conductor by means of automatic switching circuits of the type disclosed in the above-identified application of Malthaner. Relay |05, in operating, completes an obvious circuit for operating the message register |113 for recording the total r number of calls. Relay |05 in operating interrupts the holding circuit of relay |44 and permits relay lli to start to release. Relay |44 is, however, a slow-release relay and requires appreciable time to become fully released.

The operation of relay |05 removes ground from a conductor extending to the automatic volume control circuit l This ground normally maintains the gain of the volume control circuit at its maximum value so that the automatic volume limiting operation is ineffective. However, upon the operation of relay |05, the automatic voliune control circuit is enabled. A short interval of time thereafter the volume control circuit has regulated the output volume so that it will be at a predetermined value substantially independently of the level of the applied signals.

The operation of relay |05 also transfers the incoming line |0| from the terminating resistor |02 to the band-pass lter H0. The band-pass filter ||0 is provided to prevent low frequency power currents, which may be supplied to actuate the calling device of the subscribers station over the subscribers loop, from interfering with 'the operation vof the receiving equipment described herein. The band-pass lter H0 also is employed to prevent high frequency signals or high frequency components of noise or other interfering signals or stray currents from interfering' with the operation of the receiving equipment described herein.

From the band-pass filter ||0 the signals are transmitted through the automatic volume control circuit The signals are transmitted in two directions from the automatic volume control circuit (l) through the recording amplifier ||2 to the magnetic recorder H3; and (2) to the controlling amplifiers in other control circuits. Asv shown in Fig. 1 the signals are first transmitted to a detector H5 which is employed to detect the incoming pulses or other signaling currents. A disabling circuit llt is provided for disabling the detector I l5 in rendering it non-responsive to the incoming pulses.

The exemplary system set forth herein is arranged to respond to and cooperate with equipment for transmitting signals of the type set forth in the above-identied applications of Malthaner, Malthaner et aland Parkinson. Briey these signals comprise a plurality of pulses separated by blank intervals or pauses to distinguish a complete set of pulses or signals representing a complete subscribers designation. These signals are transmitted over and over again from the transmitter equipment or calling apparatus and the subscribers station as set forth in the above-identified application of Parkinson.

Each complete subscribers designation usually comprises a subscribers line number which is frequently followed by a party designation where party lines are employed. In large cities or more densely populated regions the above numbers are preceded by one or more designations dening central oiiices or switching points.

In the exemplary embodiment set forth herein, it is assumed that the complete subscribers designation comprises three characters or digits designating the switching center of the called subscriber, four digits or other identifying characters designating the subscribers station, followed by one character designating the party in case of a party line. This complete designation is followed by a pause equivalent to the time required for the transmission of two of the characters or digits. The pulses as transmitted comprise substantially a single cycle of an alternating-current wave which is assumed to be of the order of 1,000 cycles. Two such pulses are required to define each character of -the digit of the complete subscribers designation.

When each of these pulses is transmitted over voice frequency communication channels and particularly when transmitted through filters and carrier current systems having bandwidths of the order described above, each pulse as received at theV receiving station and applied to the detector circuit H5 comprises a transient of a duration which is of the order of three cr three and one-half milliseconds. In other words the original pulse of one millisecond as applied to the transmission system by the subscribers equipment is lengthened so that appreciable energy is received for approximately three to three and one-half milliseconds by the receiving equipment.

vIn order to prevent the pulses from interfering with one another it is necessary to separate the pulses by a vtime interval greater than the decay time of each pulse at the receiver. Thereafter the next succeeding pulse may be transmitted. The time thereafter at which this pulse is transmitted is controlled by the character of a symbol or digit represented by the two pulses. In the exemplary embodiment set forth herein, it is assumed that the second or stop pulse of each digit will be transmitted in any one of a plurality of times succeeding one another by approximately a half millisecond. In one specific embodiment each of these times was .44 millisecond. After the final pulse is transmitted representing the magnitude of the digit or character of the symbol, the next succeeding start pulse of the following digit or character is transmitted approximately three and one-half to four milliseconds after the final possible position of the stop pulse.

In order to more readily refer to the time required for each of the digits to be transmitted, this time has been divided up into 25 divisions or units of approximately a half-millisecond duration. In addition eight such units are allowed for each of the pulses to be received and decay to such a value that they will not interfere with the next succeeding pulse. Such an arrangement permits ten different digits or symbols to be represented in each one of the digit intervals. As pointed out above eight such digit intervals are required in the exemplary embodiment set forth herein to represent a complete subscribers designation. They are followed by a blank or pause of two such intervals so that the complete subscribers designation is completed in ten of such intervals.

A disabling multivibrator ||B is arranged so that it will disable the detector H5 for approximately three and one-half milliseconds or seven of such intervals. This renders the detector circuit less subject to false operation by noise and other stray signals and thereby improves the operation of the system. Thus after each pulse is received by the detector |5 the disabling multivibrator ||6 operates and` disables the detector for an interval of time during which the transients resulting from the pulse die out. The output of the detector ||5 is transmitted to start circuit l2| and to a gate circuit lll. The start circuit |2| is employed to respond to the incoming pulses and recognize the long pause occurring between the pulses designating the called subscribers station. Until the long pause is received and recognized by the start circuit, the gate circuit ll' is rendered ineffective.

On the recognition of the pause between the signals representing complete subscriber designations the start circuit |2| conditions the steering circuit |25 so that it will properly direct the information of the rst pulses to the proper registering or recording circuit |21. The start circuit ltd also conditions the gate circuit so that it will properly direct the pulses received by the detector circuit I l5 to the pulse absorbing circuit H8.

In the meantime, however, as pointed out above, the incoming signals from the volume limiting amplifier l|| are transmitted through a recording amplifier H2 and applied to a delay apparatus. This delay apparatus is arranged to provide a plurality of different delay intervals which intervals are equal to or a function of the expected possible different time intervals between the signals or pulses. This delay apparatus may take any suitable form such as a tapped delay line or network, a plurality of different delay networks, recording andvstorage devices or a mag- 4 fl i) v8 netic device as set forth in the exemplary embodiment of this invention set forth herein.

This magnetic recording device l 3 operates in substantial synchronism with the incoming signals and records all of the signals applied to it. These signals are stored for a short interval of time and then erased after which additional signals may be then stored in the same magnetic material. The magnetic storing device is shown in detail in Fig. 5. The magnetic material comprises a disc '50| which is continuously operated by synchronous or other type of speed regulated motor and is provided with erasing magnet 5|ll and a plurality of recording and pick-up magnets. These magnets are spaced around the periphery of the disc 50| so that a recorded signal stored in the disc travels a distance accurately related to the possible times at which pulses may be transmitted over the system.

Referring now to Fig. 5, a continuously rotating disc 50| consists of magnetic material suitable for recording magnetic conditions therein. The disc 50| is continuously rotated by a synchronous motor or by any other suitable device, motor or mechanism (not shown) at a uniform precalculated speed.

Magnetic material of the type suitable for use in magnetic recording of electrical signals are frequently called hard magnetic materials because they are mechanically hard and have a relatively high residual induction usually called Br and a relatively high coercive force He. As shown in the drawing the disc 50| is rotated past the erasing head 5H) which comprises a permanent magnet and pole-pieces 5H by which the field of the permanent magnet is conveyed to the periphery of the rotating disc 56d. The field from the permanent magnet induced in the rotating disc 56| should saturate the disc sufficiently to erase all previous magnetic variations within the magnetic material of the disc and leave the material magnetized with the residual magnetic induction oriented tangential to the disc. During the time that each portion of the disc is in the field of the permanent magnet of the erasing head and after it leaves the field of the erasing head the direction of magnetization of each elemental recording portion of the disc is indicated by the arrow SI2 in Fig. 5 and by arrow 5|?? in Fig. 5A. The uniformly magnetized portions of the periphery of the disc then pass through the recording head or between the pole-pieces of the core of coil 5|3. At this time a transverse magnetic field is induced in the disc at right angles to the direction of magnetization 5|2. The transverse eld is induced by coil EEZ as will be evident by examination of the drawing. The coil 5|2 has pole-pieces adjacent opposite sides of the disc and causes a eld to be induced between these pole-pieces either vertically upward or vertically downward as viewed in Fig. 5 and thus at right angles to the direction of rotation of the disc and at right angles to the residual magnetic induction in the magnetic material of the disc. As a result the residual magnetism within the disc is rotated in either direction as the material of the disc leaves the recording head 5|3. When the magnetic field is upward in the recording coil 5|3, the magnetic induction within the magnetic material of the disc is rotated in a counter-clockwise direction such as illustrated by the arrow 5M of Fig. 5A. When the magnetic field due to the recording coil 5i3 is downward, the magnetic induction within the material of the disc after it leaves the recording field is rotated downward as shown by the dotted arrow 5|5.

It is thus evident that the magnetic eld within the material of the disc as oriented by the recording head has a vertical component which may be in either direction and which vertical component may be employed to generate voltages in pick-up heads in a known manner.

It is also evident that elds due to both positive and negative currents are recorded in the disc by moving the magnetic vector or direction of magnetization in the disc in opposite directions. Consequently no bias is required. Itis evident that in such-an arrangement the relation between applied recording iield and the recorded eiTect is relatively linear over a wide range of magnetic amplitudes and thus over a wide range. of signal amplitudes applied to the recording head.

It has been assumed in the foregoing description that the disc of the magnetic material 'c'l is solid and made up entirely of magnetic material. It is to be understood, of course, that any suitable structure of suitable magnetic material for recording signals may be employed including discs, ribbons or other structures which are either solid and comprise essentially all magnetic material or they may comprise electrodeposited or otherwise plated metals or alloys, either in the form of discs, ribbons or the like. In addition, the disc or other form of magnetic material may consist of one of various magnetic oxides and other magnetic powders incorporated on a paper or lm base or have any other suitable structure or may be of any other known type of magnetic recording material, In addition, other forms of wipe-out methods and apparatus may be employed.

As shown in Fig. 5, after passing recording head |3 the magnetized material of the disc 58| passes between the pole-pieces of a pick-up head 520 and then successively past the pole-pieces of ten different pick-up devices or heads. Each pick-up device, in the exemplary embodiment, comprises a magnetic core with pole-pieces which extend adjacent to the periphery of disc 591. The pole-pieces are usually of thin magnetic material located so that the thickness or smallest dimension is parallel to the direction of motion of the magnetic recording medium. Each core is also provided with two windings connected as shown in the drawing to the other elements of the signal receiver described hereinafter.

The spacing between the various pick-up leads determines the actual time delay of the signals because with wider spacing more time is required for an elemental portion of the disc to pass from the pole-pieces of one pick-up to the pole-pieces of the neXt pick-up. Thus, the spacing between the reference pick-up 52 and the first one of the digit pick-ups 52| is equivalent to the time required for a pulse and its related transient to die out and be reduced to such a value that it does not interfere with any of the succeeding pulses. The spacing between each of the code or digit pick-up coils 52| to 53d inclusive, is approximately half a millisecond or in other words equivalent to the time dierence assigned to digits of different magnitudes.

Thus, assume that a start pulse is recorded by the recording coil and a stop pulse is subsequently recorded in the tenth or zero position. The start pulse then passes under the reference pick-up coil 520 and induces voltages in the windings of this coil. The recorded start pulse will then pass successively between the pole-pieces of each of the digit pick-up coils 52| to 530. When this start pulse passes through the pole-pieces of the zero coil 539 the stop pulse will be passing between the pole-pieces of the reference pick-up coil 520.

If, as assumed for the second digit the stop pulse arrives during the fourth digit interval, indicating a magnitude of four for the second digit, then the start pulse of the second digit will be passing under the fourth digit pick-up coil 524 at the time the stop pulse of the second digit is passing between the pole-pieces of the reference pick-up coil 520.

Referring now to Fig. 1, incoming signals from line itil are transmitted through the band-pass filter H0 and the automatic volume control circuit ||i and applied both to the magnetic recorder through the recording amplifier and to the detector circuit H5. rIhe detector circuit is controlledby the disable multivibrator H6 so that it cannot respond to pulses closer together in time than approximately three and one-half to four milliseconds. The output of the detector is applied to the start circuit |2i and to the gate circuit il'i. The gate circuit, however, at this time is closed so that the pulses applied to it perform no useful function. The pulses from the detector ||5 are applied to the start circuit and maintain the start circuit in its initial condition until the pause or blank interval between the groups of signals representing complete subscribers designations are received.

When this blank interval is received, start circuit |2| responds to it near its end and conditions the steering circuit |25 so that it will direct the information received `during the succeeding digit interval to the A digit register i21.

The start circuit in responding to the blank interval near the end thereof conditions the gate circuit so that it will transmit pulses from the detector circuit H5 through it to the pulse absorbing circuit H8. The first start pulse thereafter, which will be the first start pulse of a complete subscribers designation, is then transmitted through the gate circuit lil to the pulse absorbing circuit H8. The pulse absorbing circuit |i8 absorbs this pulse. The pulse, however, is recorded by the magnetic recorder as described above, thereafter, the start pulse passes the reference pick-up and induces a voltage in it, but the reference amplifier is rendered ineffective at this time so that it does not respond to this voltage. The start pulse then passes between the various other digit pick-up coils in succession and induces voltages in these coils. However, the integrating apparatus as well as the reference amplifier are unresponsive to voltages induced in the pick-up coils until a stop pulse is received.

A stop pulse, of course, will be received at some time before the start pulse has passed between the pole-pieces of the last of the digit pick-up coils.

Upon reception of the stop pulse, the detector H5 responds to it and the pulse passes through the gate circuit ||7 to pulse absorbing circuit H8. Pulse absorbing circuit ||8 does not absorb the stop pulse. It merely absorbs the start pulses. A pulse is transmitted from the pulse absorbing circuit H8, upon the reception of the stop pulse, to the integrating control circuits |22. The integrating control circuit conditions the integrating circuits through the reference amplier lll so that the integrating circuits integrate the rectified output of each of the pickup coils. These integrating circuits in this eX- Vern-plary embodiment comprise full-wave rectifier circuits which are employed to charge condansers.

When the integrating control circuit |22 is actuated to cause the integrator ||4 to integrate, the output of each of the pick-up coils, the recorder stop pulse is starting to pass through the pole-pieces of the reference pick-up coil 520 and the start pulse is likewise starting to pass through the pole-pieces of some one of the digit or channel pick-up coils. The reference amplifier is rendered active at this time and connected to all of the potential pick-up coils in such a manner that the voltage induced in the pick-up coil where the start pulse is starting to induce a voltage therein is in opposition to the voltage applied thereto from the reference amplifier so that the two voltages tend in a large measure to cancel one another. In all of the other pickup coil circuits, the iull magnitude of the stop voltage pulse is applied to the integrating circuits with the result that a large voltage is built up across the condensers associated with all but one of the channel integrating circuits. The integrating time interval, that is, the time during which the integrating control multivibrator |22 renders the integrating circuits and reference amplifiers effective may be of any suitable period. In the exemplary embodiment set forth herein this period is the time interval of a received pulse, that is, from three and one-half to four milliseconds or eight of the increments or units, described above, out of the digit interval assigned to the digit. At the end of 'this time interval, the integrating circuits and reference amplifier are again rendered unresponsive to signals from the magnetic recording devices and a read vpulse is generated in the read circuit |23. This pulse is applied to a recycle circuit |20 and also to the integrating circuits I lil. This pulse causes the integrator which has a voltage less than a predetermined amount stored upon it from an integrating condenser to actuate storing apparatus and if the storing apparatus associated with more than one of the digital channels is actuated or if none of such apparatus is actuated then the recycle circuit |26 is set into operation and the circuits reconditioned to respond to the next blank interval in the manner described above. However, if the storage apparatus associated with only one of the integrating devices is actuated is response to the read pulse the equipment is not recycled. The end of the read pulse reset circuit |24 is actuated which restores the charge in the integrating circuits to their initial values so that they will be available for use in responding to the succeeding pulses of the succeeding digit. During the read interval, as described above, the output of the integrator circuits are also transierred to the register circuit |26 which may comprise any suitable number of registers. As shown in the drawing, three such registers have been provided and the operation of the integrating circuit in response to the start and stop pulses of the iirst digit after the blank interval will be stored in the register circuit |21. In the specic embodiment set forth herein this register circuit is arranged to translate the code representing the various digits.

Thereafter, the next start pulse will be received and actuate the circuits in the manner similar to that described above. The next stop pulse which Will be the second one will again actuate the circuits and cause the integrating circuits ||4 to operate in the manner described above. At this time the steering circuit |25 will cause the information to be recorded in the translating and recording circuit |28. The information of the succeeding digits will be transmitted to and recorded by the succeeding registers such as |29, and any additional registers for recording additional digits which may be required for control of the circuits at any of the switching centers. If the recording and storing devices associated with one and only one of the various integrating devices respond to each digit, the steering circuit at the end of the reception of the number of digits required actuates disabling circuit ||6 so that it will disable detector H5 and prevent it from responding to subsequently received pulses. In addition, the digit steering circuit causes relay |42 to be actuated, which relay causes circuits to respond to transfer the setting of the registers in register circuit |26 to the register circuits |30 to |32, inclusive. The output of these registers may be observed by means of lamps and checked by checking relays and keys |33. The checking relays and keys |33 comprise a group ci keys which are set in accordance with the expected subscribers number or station designation. The relays are operated in accordance with the recorded designation. If the relay corresponding to the operated keys and only the corresponding relays operate one circuit is completed by this equipment |33; otherwise another circuit is completed by it.

If the code has been properly received. the OK register ISQ is actuated which causes relay |31 and in turn relays |38 and |45 to be operated. Relay M5 in operating causes the circuits of the system to be restored to the conditions in which they were after the rst pulse is received after the system is connected to a subscribers line. If the several digits for which the keys have been set have not properly been received, the error register |35 is actuated and provided key I'l is operated to the position shown the circuit will again advance as described above. If, however, key mi has been operated, the system will stop in response to an error and may be advanced only by operating key m6 whereby the circuits are advanced as described above, and are then in condition for responding to another series of pulses representing a complete designation of the called subscriber.

If the integrating circuits do not respond to the read pulse in the proper manner, that is, if the recording equipment is associated with more than one integrating device or if none of these recording equipments respond to the read pulse then the entire circuit is recycled and the previously recorded digits are discarded. Thereafter the circuits will respond to a succeeding group of pulses representing the complete designation of the called subscriber in the manner set forth above. The digital indications stored in the register circuitslt, |3| and |32 or the registering and translating circuits |21, |28 and E29 may be employed to actuate automatic switching equipment selectively in any desired or suitable manner. One such arrangement is described in the above-identified application of Malthaner.

The above described operation as generally described, may be more readily understood from the following description in detail, of the elemental details of the system shown in Figs. 3 through l2 when arranged adjacent one another as shown in Fig. 2 and also with reference to Figs. 13 and 14 which show graphically the current and voltage conditions at various places in the system.

Assuming now that the calling transmitting device 33! of the subscriber station has been connected over the subscribers line 302 to the terminal and switching equipment 303 to the receiving apparatus shown in Fig. 3. The terminating and switching equipment may include any suitable types of manual or automatic switching circuits, apparatus or systems. It is further assumed that ground is applied to conductor 90I either by means of key 902 or by means of the switching equipment which connects the receiver to the subscribers line such as represented by 303. When ground is applied to conductor 90| the circuit is completed for the operation cf relay BI@ from the ground connected to conductor 30! through the lower break contacts of relay 8I4 and the upper break contacts of relay SI to battery through the winding of relay 890. Relay 8I0 operates and interrupts the operating circuit of relay 812 which relay thereupon releases after a short interval of time. Relay 8I0, operated, completes an obvious circuit for the operation of the total calls register 316 which records the total number of calls received by the equipment shown in Figs. r3 through 12, inclusive. Operation of relay 8I0 also removes the terminating resistance SH3-from the incoming line and connects the transmission path from the terminal equipment 303 to the band-pass filter 304 so that the subsequent signals will be transmitted through this lter to the terminating resistance 305 and also through the input transformer 3 I0 to the amplifier equipment shown in Fig. 3.

Operation of relay 3I0 also removes ground from the conductor SI'I which extends through Figs. 7, 6, 5 and 4 to the upper terminal of condenser 3I8 of Fig. 3 through resistor 331. When ground is removed from the upper terminal of condenser SIB, it may assume a negative charge or potential as will be described hereinafter.

Assume further that the calling device 30| is supplied with suitable power either locally or over the subscribers line, means for doing this being known and that this calling device is set into operation and repeatedly transmits signals of the type described above representing the designation of a called subscribers station. These signals are then transmitted over the line 302 and then through switching and interconnecting equipment 303 to the band-pass lter 304 through the operated contacts of relay 8I0.

The subscribers line 302 may comprise any suitable type of subscribers line and related equipment capable of transmitting voice frequency signaling currents and any other necessary or desirable supervisory or control currents, these being known. The switching equipment 303 may include any suitable types of switching equipment including manually operated switchboards, automatic switching systems operated under control of dial produced or other types of signaling pulses. Equipment 303 may include other suitable types of interconnecting equipment including toll lines, voice frequency channels of carrier current systems, radio systems and suitable combinations of said systems together with the necessary control and interconnecting equipment. Usually, however, terminal equipment and circuits 303 will include automatic switching equipment as well as a communication path through it to the receiving equipment to be described herein in detail. Y

The band-pass filter 304 is arranged to pass a frequency band of approximately 300 to 2000 cycles. This band-pass filter accomplishes two purposes. In the first place by suppressing the high frequency currents the operation of the system is made more reliable and less susceptible to misoperation by noise currents which have high frequency components. In addition the lower cut-off of the filter prevents interference from the low frequency. power currents which may be transmitted over the subscribers line to the subset for actuating the calling device located thereat. In these cases the low-pass filter 304 eifectively prevents these power frequencies from interfering with the operation of the receiving equipment set forth herein in detail. In case power is not supplied over the signal path, the lower cut-off of the filter still serves to prevent noisev interference.

The band-pass filter 304 is terminated by matching resistor 305 and the transformer 3|0 having two balanced secondary windings. Incoming pulses are applied to the control elements of tubes 3I I and 3I2 in push-pull or phase opposition by means of transformer 3I0.

Normally, condenser 3 I8 is discharged through break contacts of relay 8I0 between calls. However, upon the operation of relay Slt as described above, ground is removed from the upper terminal of this condenser which will be charged in the manner described hereinafter. However, so longas condenser :BIS is not charged the gains of-the amplifier tubes 3II and 3I2 are maintained at their maximum value.

Tubes 3 II and 3I2 consequently repeat the received signals through the output transformer 3 I3. The signals are then applied to the recording amplifier shown in Fig. 4 and to the rectifierelem'ents 3I4 and SI5. Rectifier elements 3I4 and 3 I5 are arranged in a full wave rectifier circuit.

These rectifier elements are designated in the drawing as comprising any suitable non-linear rectifier element including copper oxide, selenium, silicon, germanium, etc. These rectifier elements, however, may also comprise any suitable types of tubes including gas-lled tubes and also high vacuum diodes.

By employing two such rectiflers arranged in a full wave rectifier, both the positive and negative portions of the received signals are rectified and contribute to the output of these rectiers. As a result, whichever one of the positive and negative portions of the received signals is largest will cause the greatest output voltage.

The output voltage from the rectifiers 3I4 and 3I5 is connected to the input of the cathode followertube 3I6. Tube 3I6 is provided as an isolation tube and to reduce the current load on the rectiers 3I4 and 3 I5. The output of these rectifiers as supplied to the control element of 4tube 3I6 is positive with respect to ground so that a positive yvoltage above ground is repeated in the cathode circuit of tube 3I6 in response to each of the received pulses. The cathode of tube 3I6 is connected through a suitable network comprising condenser 325 to the control element of the righthand section of tube 3I'I. The control element of this tube is biased negatively by means of pctentiometer 324 so that no current normally ows through the right-hand section of tube 3I 'I.

However, when the amplified output of tubes 3| I and 3 I2 as rectified by the rectiers 3I4 and 3 I 5 exceeds vthe bias determined by potentiometer 324, current tendsto row in the youtput circuit 

